Cardiovascular autonomic effects of electronic cigarette use: a systematic review

Abstract

Purpose: Electronic cigarettes (ECs) are the fastest growing tobacco product in the USA, and ECs, like tobacco cigarettes (TCs), have effects on the cardiovascular autonomic nervous system, with clinical implications. The purpose of this review was to collect and synthesize available studies that have investigated the autonomic cardiovascular effects of EC use in humans. Special attention is paid to the acute and chronic effects of ECs, the relative contributions of the nicotine versus non-nicotine constituents in EC emissions and the relative effects of ECs compared to TCs.

Methods: Using the methodology described in the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) statement, we conducted a literature search of the Ovid PubMed and Embase databases on 6 December 2019 using keywords in titles and abstracts of published literature. Acute (minutes to hours) and chronic (days or longer) changes in heart rate variability (HRV), heart rate (HR) and blood pressure (BP) were used as estimates of cardiovascular autonomic effects.

Results: Nineteen studies were included in this systematic review, all of which used earlier generation EC devices. Acute EC vaping increased HR and BP less than acute TC smoking. Nicotine but not non-nicotine constituents in EC aerosol were responsible for the sympathoexcitatory effects. The results of chronic EC vaping studies were consistent with a chronic sympathoexcitatory effect as estimated by HRV, but this did not translate into chronic increases in HR or BP.

Conclusions: Electronic cigarettes are sympathoexcitatory. Cardiac sympathoexcitatory effects are less when vaping using the earlier generation ECs than when smoking TCs. Additional studies of the latest pod-like EC devices, which deliver nicotine similarly to a TC, are necessary.

Keywords: Autonomic nervous system; Electronic cigarettes; Nicotine; Smoking; Sympathetic nervous system; Vaping.

Fig. 1

PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analysis) study selection process. The electronic search yielded 224 studies, of which 53 were removed because they were found to be duplicates, and 132 studies were excluded because they either did not meet the inclusion criteria (n = 115) or a full text was not available (n = 17). A full-text review of the remaining 39 studies then led to the exclusion of 21 studies because one study was an editorial and 20 studies had no relevant outcome measures. One additional study [18], published after the literature search, was included while the paper was under review. A total of 19 studies were included in this qualitative systematic review

Fig. 2

Summary of acute hemodynamic effects of smoking tobacco cigarettes (TCs) versus electronic cigarette (EC) vaping. Data are from 11 comparisons of the acute effects of ECs and TCs on hemodynamic parameters and show that the effects of ECs with nicotine on systolic blood pressure (SBP; a), diastolic BP (DBP; b) and heart rate (HR; c) were significantly less than those of TCs. The forest plot of each study represents the mean differences between TCs and ECs, with the corresponding lower and upper 95% confidence bounds. Plots to the right of the vertical dashed line, which represents no effect, indicate that the effect of TC smoking is worse than than that of EC vaping. The letters A–E in the Yan studies represent different EC devices, and the X represents the TC exposure

Fig. 3

Summary of acute hemodynamic effects of electronic cigarettes with nicotine compared to electronic cigarettes without nicotine. Data from 5 acute studies revealed that the effects of EC with nicotine compared to ECs without nicotine on SBP (a), DBP (b) and HR (c) were significantly less. The forest plot entry for each study is the mean differences between ECN and EC0, with the corresponding lower and upper 95% confidence bounds. The plots to the right of the vertical line of no effect indicate that ECN is worse than EC0. DBP diastolic blood pressure, ECN electronic cigarette with nicotine, EC0 electronic cigarette without nicotine, HR heart rate, SBP systolic blood pressure, TC tobacco cigarette

Fig. 4

Boxplot of heart rate variability in chronic EC vapers compared to age-matched controls. a The high-frequency (HF) component, an indicator of vagal activity, was significantly decreased in the EC vapers compared with non-user control individuals (mean [SEM] 46.5 [3.7] vs. 57.8 [3.6] nu; p = 0.04). b, c The low-frequency (LF) component, an indicator largely of sympathetic activity (mean [SEM] 52.7 [4.0] vs. 39.9 [3.8] nu, p = 0.03), and the LF to HF ratio (1.37 [0.19] vs. 0.85 [0.18]; p = 0.05), were significantly increased in the EC users compared with the non-user controls. These results are consistent with sympathetic predominance. These findings were present even in the absence of recent EC use, as verified by the absence of detectable nicotine in the plasma. SEM Standard error of the mean. Filled circles represent the mean, horizontal lines represent the median. Used with permission from Moheimani et al. [35], copyright 2017, American Medical Association